Person support apparatus with actuator brake control

ABSTRACT

A person support apparatus includes one or more motorized actuators that are braked in different manners depending upon whether or not electrical power is available to the control system. When electrical power is not available, a delay circuit delays closing a first switch that, when closed, short circuits the terminals of one of the motors. When power is available, other switches are opened and closed in a manner that short circuits the terminals of the motor while the first switch remains open. The other switches may be part of an H-bridge. The control system may also detect back emf (electromotive force) generated by the motor when electrical power is available and issue a notification to a technician or other user if an amplitude and/or duration of the detected back emf exceeds a threshold.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/838,693 filed Aug. 28, 2015, by inventors Daniel Vincent Brosnan etal. and entitled PERSON SUPPORT APPARATUS WITH ACTUATOR BRAKE CONTROL,and claims priority to U.S. provisional patent application Ser. No.62/053,498 filed Sep. 22, 2014 by inventors Daniel Brosnan et al. andentitled PERSON SUPPORT APPARATUS WITH ACTUATOR BRAKE CONTROL, thecomplete disclosures of both of which are hereby incorporated herein byreference.

BACKGROUND

The present disclosure relates to person support apparatuses, such as,but not limited to, beds, cots, stretchers, recliners, chairs, operatingtables, and the like; and more particularly to the control of one ormore actuators on the person support apparatus.

Person support apparatuses often include one or more actuators formoving one or more components of the person support apparatus. Forexample, beds used in medical facilities often include a headsection—sometimes referred to as a Fowler section—that is pivotablebetween a generally horizontal orientation and a raised orientation,thereby allowing an occupant thereof to move between lying flat andsitting upright. As another example, recliners often include one or moreactuators for pivoting a backrest and/or for extending and retracting aleg rest. Regardless of the specific person support apparatus they areincorporated into, such actuators often also act as a brake upon themovement of the component when the actuator is not being actuated. Thatis, the actuator may act as a brake and resist movement of the componentwhen the actuator is not being activated.

SUMMARY

In at least one embodiment, the present disclosure provides an improvedsystem and/or method for controlling an actuator on a person supportapparatus that provides greater braking force than would otherwise byachieved by simply removing electrical power from the actuator. Thegreater braking force means that the movable component controlled by theactuator is less likely to move when the actuator is not actuated,thereby reducing the possibility that a controller of the actuator willlose track of the current position of the actuator. The greater brakingforce also provides improved safety by preventing movement in situationswhere movement is not intended.

According to one embodiment, a person support apparatus is provided thatincludes a support surface adapted to support a person thereon, anactuator, a motor, and a control system. The actuator is adapted to movea first component of the person support apparatus with respect to asecond component. The motor is adapted to power the actuator. Thecontrol system is adapted to brake the motor in a first manner whenelectrical power is supplied to the control system and to brake themotor in a second manner when electrical power is not supplied to thecontrol system, wherein the first and second manners are different.

According to other embodiments, the control system delays braking themotor in the second manner for a predetermined time after electricalpower is not supplied to the control system. In at least one embodiment,the predetermined time is based on a resistor-capacitor (RC) circuit.

In another embodiment, the first manner is a software controlled brakingand the second manner is a hardware controlled braking.

In another embodiment, the control system uses a plurality of solidstate switches for the first manner and either a solid state relay or anelectromechanical relay for the second manner. The plurality of solidstate switches include a plurality of field effect transistors (FETs) inat least one embodiment.

In at least one embodiment, the control system brakes the motor in thefirst manner by short circuiting terminals of the motor using aplurality of switches, and the control system brakes the motor in thesecond manner by short circuiting the terminals of the motor using aswitch different from the plurality of switches.

The controller is a microcontroller in at least one embodiment thatcontrols a plurality of switches. The microcontroller controls theplurality of switches so as to short circuit terminals of the motor inorder to brake the motor in the first manner. A relay that is notcontrolled by the microcontroller short circuits the terminals of themotor in order to brake the motor in the second manner.

In some embodiments, the control system does not brake the motor in anyother manner besides the first and second manners.

According to another embodiment, a person support apparatus is providedthat includes a base having a plurality of wheels, a support surface, anactuator, a motor, and a control system. The support surface is adaptedto support a person thereon and includes a backrest section, a seatsection, and a leg section. The actuator moves at least one of thebackrest, seat, and leg sections with respect to another of thebackrest, seat and leg sections. The motor is adapted to power theactuator, and the control system brakes the motor by short circuitingterminals of the motor.

In other embodiments, the actuator is adapted to pivot the backrestsection with respect to the seat section. In still other embodiments,the person support apparatus includes a second actuator adapted to movethe leg section with respect to the seat section, and the secondactuator includes a second motor adapted to power the second actuator.The control system is also adapted to brake the second motor by shortcircuiting the terminals of the second motor.

In other embodiments, the control system is adapted to short circuit themotor in two different manners: a first one when electrical power issupplied to the control system, and a second one when electrical poweris not supplied to the control system.

The control system includes an H-bridge circuit having four switches inat least one embodiment, and the first manner includes closing at leasttwo of the four switches. The second manner used by the control systemshort circuits the motor regardless of the open or closed states of thefour switches.

According to another embodiment, a person support apparatus is providedthat includes a base, a support surface, a first actuator, a secondactuator, and a control system. The support surface is adapted tosupport a person thereon and includes a seat, a backrest, and a legrest. The first actuator has a first motor adapted to pivot the backrestwith respect to the seat, and the second actuator has a second motoradapted to pivot the seat with respect to the base. The control systembrakes the first and second motors in a first manner when electricalpower is supplied to the control system and brakes the first and secondmotors in a second manner when electrical power is not supplied to thecontrol system. The first and second manners are different.

In another embodiment, the person support apparatus includes a thirdactuator having a third motor adapted to change the height of the seatrelative to the base, and a fourth actuator having a fourth motoradapted to pivot the leg rest with respect to the seat. The controlsystem brakes the third and fourth motors in the first manner whenelectrical power is supplied to the control system and brakes the thirdand fourth motors in the second manner when electrical power is notsupplied to the control system. In some embodiments, the control systemdelays braking the first and second motors in the second manner for apredetermined time after electrical power is not supplied to the controlsystem.

In still other embodiments, the first motor is included in a firstH-bridge having four switches, and the second motor is included in asecond H-bridge having four switches. The first manner includes closingat least two of the four switches of the first H-bridge and closing atleast two of the four switches of the second H-bridge. The second mannershort circuits each of the first and second motors regardless of theopen or closed states of the four switches of the first H-bridge andregardless of the open or closed states of the four switches of thesecond H-bridge.

In at least one other embodiment, the control system includes amicrocontroller for changing the states of the four switches of thefirst H-bridge and for changing the states of the four switches of thesecond H-bridge. The control system further includes a first relay forshort circuiting the first motor when electrical power is not suppliedto the control system and a second relay for short circuiting the secondmotor when electrical power is not supplied to the control system.

The control system is adapted in one or more embodiments to detectback-emf created by the motor when the motor is not being driven. Suchback-emf is created when a force is applied to the component of theperson support apparatus that is moved by the motor. The detectedback-emf is repetitively compared to one or more threshold values todetermine if its amplitude, an integral of its amplitude, or anotherquantity based on its amplitude exceeds one or more thresholds. If sucha threshold is exceeded, the controller issues a notification of apotential error.

In any of the embodiments disclosed herein, the person support apparatusmay be a recliner or a bed.

Before the various embodiments disclosed herein are explained in detail,it is to be understood that the claims are not to be limited to thedetails of operation, to the details of construction, or to thearrangement of the components set forth in the following description orillustrated in the drawings. The embodiments described herein arecapable of being practiced or being carried out in alternative ways notexpressly disclosed herein. Also, it is to be understood that thephraseology and terminology used herein are for the purpose ofdescription and should not be regarded as limiting. The use of“including” and “comprising” and variations thereof is meant toencompass the items listed thereafter and equivalents thereof as well asadditional items and equivalents thereof. Further, enumeration may beused in the description of various embodiments. Unless otherwiseexpressly stated, the use of enumeration should not be construed aslimiting the claims to any specific order or number of components. Norshould the use of enumeration be construed as excluding from the scopeof the claims any additional steps or components that might be combinedwith or into the enumerated steps or components.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of one embodiment of a person supportapparatus according to one aspect of the present disclosure;

FIG. 2 is a side elevational view of the person support apparatus ofFIG. 1 with several components removed in order to illustrate aplurality of actuators incorporated into the person support apparatus;

FIG. 3 is a block diagram of an actuator control system for one of theactuators of the person support apparatus of FIG. 1;

FIG. 4 is a state table illustrating the states of the actuator controlsystem of FIG. 4 based on the state of the switches of the controlsystem;

FIG. 5 is an electrical schematic of an embodiment of an H-bridgecircuit for implementing the actuator control system of FIG. 3;

FIG. 6 is an electrical schematic of a first embodiment of a motorcircuit that may be coupled to leads A and B of the circuit of FIG. 5;

FIG. 7 is an electrical schematic of a second embodiment of a motorcircuit that may be coupled to leads A and B of the circuit of FIG. 5;

FIG. 8 is an electrical schematic of a voltage sensing circuit that iscoupled, in some embodiments, to the leads A and B of the circuit ofFIG. 5; and

FIG. 9 is an electrical schematic of an alternative voltage sensingcircuit that is coupled, in some embodiments, to one of the leads A andB of the circuit of FIG. 5.

DETAILED DESCRIPTION OF THE EMBODIMENTS

A person support apparatus 20 according to one embodiment is shown inFIG. 1. Person support apparatus 20 is shown in FIG. 1 to be a recliner.Although the following written description will be made with respect toa recliner, it will be understood by those skilled in the art that theprinciples disclosed herein may also be incorporated into other types ofperson support apparatuses besides recliners, such as, but not limitedto, beds, stretchers, cots, surgical tables, chairs, or the like.

Person support apparatus 20 includes a seat 22, a backrest 24, a legrest 26, a pair of armrests 28, and a plurality of wheels 30. Personsupport apparatus 20 is constructed such that both the height and tiltof seat 22 is adjustable. Further, person support apparatus 20 isconstructed such that backrest 24 is pivotable between a generallyupright position, such as shown in FIG. 1, and a virtually infinitenumber of rearwardly reclined positions. Leg rest 26 is constructed suchthat it is able to be moved between a retracted position, such as shownin FIG. 1, and an extended position, in which leg rest 26 is orientedgenerally horizontally and extends forwardly from seat 22. Armrests 28,in the illustrated embodiment, are constructed such that a user canraise and lower their height relative to seat 22.

In at least one embodiment, it will be understood that person supportapparatus 20 may be constructed in accordance with any of theembodiments disclosed in commonly assigned, copending U.S. patentapplication Ser. No. 14/212,253 filed Mar. 14, 2014 by inventorsChristopher Hough et al. and entitled MEDICAL SUPPORT APPARATUS, thecomplete disclosure of which is incorporated herein by reference. Themovement and control of person support apparatus 20 may also be carriedout in accordance with the disclosure of commonly assigned, copendingU.S. provisional patent application Ser. No. 62/029,142 filed Jul. 25,2014 by inventors Anish Paul et al. and entitled MEDICAL SUPPORTAPPARATUS, the complete disclosure of which is also incorporated hereinby reference. Person support apparatus may also be constructed in othermanners besides those described in these two commonly assigned patentapplications.

FIG. 2 shows various internal components of person support apparatus 20,including a seat actuator 32, a backrest actuator 34, a lift actuator36, and a leg rest actuator 38. Each of actuators 32, 34, 36, and 38 aremotorized linear actuators that are designed to linearly extend andretract under the control of a controller. Seat actuator 32 includes astationary end 40 that is pivotally mounted to a chassis 42 of personsupport apparatus 20. Seat actuator 32 further includes an extendibleend 44 that is pivotally mounted to a seat frame 46. When seat actuator32 extends or retracts, extendible end 44 causes seat frame 46 to pivotabout a seat pivot axis 48. The extension of seat actuator 32 thereforecauses seat frame 46 to tilt in such a manner that a forward end of seat22 moves downward relative to a backward end of seat 22 (i.e. seat frame46 will rotate in a counterclockwise direction as shown in FIG. 2). Theretraction of seat actuator 32 will, in contrast, cause seat frame 46 totilt in the opposite manner (i.e. seat frame 46 will rotate in aclockwise direction as shown in FIG. 2).

Backrest actuator 34 includes a stationary end 50 that is mounted tobackrest 24 and an extendible end 52 that is mounted to seat frame 46.The extension and retraction of backrest actuator 34 will thereforecause backrest 24 to pivot with respect to seat frame 46. Morespecifically, when backrest actuator 34 extends, backrest 24 will rotatein a counterclockwise direction in FIG. 3. In contrast, when backrestactuator 34 retracts, backrest 24 will rotate in a clockwise directionin FIG. 3. Because backrest 24 is coupled to seat frame 46, the rotationof seat frame 46 by seat actuator 32 will also cause backrest 24 torotate with respect to the floor as seat frame 46 rotates. Thisrotation, however, will be independent of the rotation of backrest 24caused by backrest actuator 34. In other words, the relative anglebetween backrest 24 and seat 22 will only change when backrest actuator34 is actuated (and not when seat actuator 32 extends or retracts whilebackrest actuator 34 does not change length). The angle of backrest 24with respect to the floor (or another fixed reference), however, willchange as seat frame 46 pivots about seat pivot axis 48.

Leg rest actuator 38 includes a stationary end 65 that is mounted toseat frame 46 and an extendible end 57 that is mounted to leg rest 26.The extension of leg rest actuator 38 therefore will pivot leg rest 26from a retracted position (e.g. FIG. 1) to an extended position in frontof seat 22. The physical construction of leg rest 26 may take on any ofthe forms disclosed in the commonly assigned U.S. patent applicationSer. No. 14/212,253 mentioned above, whose disclosure is incorporatedcompletely herein by reference. Other physical constructions of leg rest26 are also possible. The extension and retraction of leg rest actuator38 will change the orientation of leg rest 26 with respect to seat frame46. The orientation of leg rest 26 with respect to seat frame 46 willnot change based on the extension or contraction of any other actuators32, 34, or 36. The orientation of leg rest 26 with respect to the floor(or some other fixed reference), however, will change when seat frame 46is pivoted about seat pivot axis 48 by seat actuator 32. In summary,then, the pivoting of seat frame 46 about its pivot axis 48 willtherefore change the orientations of all of seat 22, backrest 24, andleg rest 26 with respect to the floor (or other fixed reference), butwill not, by itself, change the orientations of any of these components(seat 22, backrest 24, and leg rest 26) with respect to each other.

Lift actuator 36 includes a stationary end 54 that is coupled to a base56 and an extendible end 58 that is coupled to an X-frame lift 60.X-frame lift 60 includes two legs 62 that are pivotally coupled to eachother about a center axis 64. When lift actuator 36 extends or retracts,the relative angle between each of the legs 62 changes, which changesthe overall height of X-frame lift 60. Further, because chassis 42 ismounted on a top end of X-frame lift, the changing height of X-framelift changes the height of chassis 42. Lift actuator 36 therefore raisesthe height of chassis 42 when it extends and lowers the height ofchassis 42 when it retracts. Because seat frame 46 is mounted(pivotally) on chassis 42, and because backrest 24 and leg rest 26 areboth mounted to seat frame 46, raising and lowering the height ofchassis 42 simultaneously raises and lowers the height of seat 22,backrest 24, and leg rest 26. However, extending and retracting liftactuator 36 does not, by itself, change the angular orientations of anyof leg rest 26, backrest 24, and/or seat 22, either with respect to eachother or with respect to the floor.

Each of the actuators 32-38 is powered by a direct current (DC)electrical motor. That is, each of the actuators 32-38 will extend orretract in response to its associated motor being driven in onedirection or its opposite direction. The control of each motor iscarried out by a control system 66. FIG. 3 illustrates the portion ofcontrol system 66 that is used to control the operation of one motor 68that is used to power one of actuators 32-38. It will be understood bythose skilled in the art that control system 66 controls each of theother three actuators in the same manner as shown in FIG. 3 anddescribed in more detail below.

Control system 66 includes a controller 70 that is in communication withmotor 68 which, as noted above, controls the extension and retraction ofa corresponding one of the actuators 32-38. Controller 70 is constructedof any electrical component, or group of electrical components, that arecapable of carrying out the functions described herein. In manyembodiments, controller 70 is a conventional microcontroller, althoughnot all such embodiments need include a microcontroller. In general,controller 70 includes any one or more microprocessors,microcontrollers, field programmable gate arrays, systems on a chip,volatile or nonvolatile memory, discrete circuitry, and/or otherhardware, software, or firmware that is capable of carrying out thefunctions described herein, as would be known to one of ordinary skillin the art. Such components can be physically configured in any suitablemanner, such as by mounting them to one or more circuit boards, orarranging them in other manners, whether combined into a single unit ordistributed across multiple units. The instructions followed bycontroller 70 in carrying out the functions described herein, as well asthe data necessary for carrying out these functions are stored in memoryaccessible to controller 70.

Controller 70 is in electrical communication with four switches 72 a-dthat, together with motor 68, define an H-bridge 74 (FIG. 3). Controller70 communicates with switches 72 a-d via lines 73 a-d, respectively. Acontrol circuit 80 is also included within control system 66 and is inelectrical communication with a fifth switch 76. A voltage source 78supplies electrical power to motor 68, depending upon the states ofswitches 72 a-d and 76, as will be described in greater detail below.Voltage source 78 may be a battery and/or it may be a rectifier or othercircuitry that receives AC power from a wall outlet via an AC powercable and provides a source of electrical current for driving motor 68.Motor 68 is, in one embodiment, a brushed DC motor.

The control of the operation of motor 68 in FIG. 3 is carried outthrough the selective opening and closing of switches 72 a-d and 76.More specifically, FIG. 4 illustrates how the state of each of theswitches 72 a-d and 76 is changed in order to carry out the control ofmotor 68. Thus, with reference to FIGS. 3 and 4, controller 70 isconfigured to drive motor 68 in a first direction by closing switches 72a and 72 d while opening switches 72 b and 72 c. This electricallycouples a voltage source 78 to the motor 68 in a positive manner,thereby driving motor 68 in the first direction. Controller 70 isfurther configured to drive motor 68 in a second and opposite directionby closing switches 72 b and 72 c while opening switches 72 a and 72 d.This switch configuration electrically couples voltage source 78 tomotor 68 in a negative manner, thereby driving motor 68 in the second,opposite direction. If it is desirable to allow motor 68 to freewheel atsome point, controller 70 effectuates this by opening all four ofswitches 72 a-d.

Control system 66 is also configured to brake motor 68 in at least twodifferent manners. In a first manner, controller 70 actively brakesmotor 68 when no movement is desired by implementing either an activelow-side brake or an active hi-side brake. The active low-side brake isimplemented when controller 70 closes switches 72 b and 72 d whileopening switches 72 a and 72 c. This effectively creates an electricalshort circuit between the terminals of motor 68. The active hi-sidebrake is implemented when controller 70 closes switches 72 a and 72 cwhile opening switches 72 b and 72 d. This also effectively creates anelectrical short circuit between the terminals of motor 68. In oneembodiment, controller 70 implements the active low-side brakingwhenever electrical power is being supplied to controller 70 and nomovement of motor 68 is desired (e.g. a user is not activating a button,or other control, that causes movement of person support apparatus 20),although it will be understood by those skilled in the art thatcontroller 70 could alternatively implement active high-side brakingwhenever electrical power is being supplied to controller 70.

As noted, control system 66 is also adapted to brake motor 68 in asecond manner. More specifically, control system 66 is configured tobrake motor 68 in a passive manner using hardware if and when electricalpower is not present. That is, if voltage source 78 is disconnected,fails, or becomes depleted, control system 66 automatically brakes motor68 in a second manner. More specifically, control system 66automatically brakes motor 68 during a loss of voltage source 78 byclosing fifth switch 76. The closing of fifth switch 76 is not carriedout by controller 70 in the illustrated embodiment. Rather, fifth switch76 is a normally closed relay that is opened by control circuit 80 whenelectrical power is supplied to control system 66 (e.g. when voltagesource 78 is functional). Fifth switch 76 may be an electromechanicalrelay, or it may be a solid state relay, or it may be some other type ofswitch. Control circuit 80 is adapted to keep switch 76 open so long assufficient electrical power continues to be supplied by voltage source78. If and when voltage source 78 fails, control circuit 80 no longerremains able to keep fifth switch 76 in an open stated, and switch 76therefore reverts to its normally closed state. In this normally closedstate, fifth switch 76 effectively short circuits the two terminals ofmotor 68, thereby braking motor 68. The braking of motor 68 by fifthswitch 76 occurs regardless of the state of any or all of switches 72 a,b, c, and/or d. In the specific embodiment illustrated in FIG. 5,switches 72 a, b, c, and d will all be open when motor 68 is braked inthe second manner due to a lack of power supplied to the transistors 72a, b, c, and d illustrated therein.

In one embodiment, such as shown in FIG. 6, control circuit 80 includesa delay circuit 90 that is configured to delay the closing of fifthswitch 76 for a fraction of a second—or longer in otherembodiments—after a power loss is experienced. This delay helps preventany damage that might otherwise occur to one or more of switches 72 a,b, c, and/or d were the closing of fifth switch 76 to occurinstantaneously after a power loss, particularly where switches 72 a, b,c, and/or d are implemented as solid state devices. Delay circuit 90 ofFIG. 6 includes a resistor 84 and a capacitor 86 coupled to one of theinputs of switch 76.

FIGS. 5 and 6 illustrate in greater detail one manner in which switches72 a, b, c, and d may be implemented, as well as fifth switch 76 andcontrol circuit 80. In the embodiment shown in FIG. 5, switches 72 a-dof H-bridge 74 are each implemented as Metal-Oxide Semiconductor FieldEffect Transistors (MOSFETs). Each MOSFET has a gate terminal that iselectrically coupled to an output of controller 70 (not shown in FIG.5). Controller 70 controls the voltage supplied to each of these gateterminals, thereby controlling the switching of each of the MOSFETs. Inone embodiment, where controller 70 is implemented as a microcontroller,the control of MOSFETs 72 is carried out via the software executed bythe microcontroller, which determines the timing of the electricalsignals supplied to the gates of each of the MOSFETs 72.

FIG. 6 illustrates in greater detail one manner of constructing a motorcircuit 82 that is coupled between terminals A and B of control system66. The content of motor circuit 82 is represented generically in FIG. 5as a box. However, two different manners of implementing this motorcircuit 82 are shown in detail in FIGS. 6 and 7 (circuit 82 a in FIG.7). Motor circuit 82 of FIG. 6 illustrates fifth switch 76, controlcircuit 80, delay circuit 90, and connections to motor 68. Delay circuit90, as noted previously, includes resistor 84 and capacitor 86 arrangedin series with each other and electrically coupled to one terminal offifth switch 76. Resistor 84 and capacitor 86 define aresistive-capacitive (RC) circuit having a time constant that isdetermined by the values of resistor 84 and capacitor 86. When voltagesource 78 is terminated, control circuit 80 will continue to supply apositive voltage to one terminal of fifth switch 76 for a time generallyequal to the RC time constant of circuit 80. This will have the effectof keeping fifth switch 76 open for a fraction of a second afterelectrical power is lost, thereby helping to prevent damage to any ofMOSFETs 72 a-d. After a time equal to or greater than the RC timeconstant passes, fifth switch 76 will return to its normally closedstate, thereby short circuiting the terminals of motor 68 and brakingmotor 68 from further movement.

When controller 70 effectuates the braking of motor 68 through eitheractive low-side or active high side braking, no voltage is applied tothe terminals of motor 68. That is, neither controller 70 nor any othercontrol circuitry applies a difference to the motor terminals in orderto generate a torque in motor 68 that resists a force being applied tothe actuator which motor 68 powers. Instead, for the active high sidebraking, voltage source 78 is applied to both terminals of motor 68; andfor the active low side braking, both terminals of motor 68 are coupleddirectly to ground. In both of these types of active braking (low andhigh), the braking power that results is due to the short circuiting ofthe motor terminals and the consequent back EMF (electromotive force)that is generated when attempts to manually turn motor 68 are made.Thus, when motor 68 is braked and a person, for example, exerts a forceon a component of person support apparatus 20 that is moved via anactuator driven by motor 68, motor 68 will resist movement of theassociated actuator and the component of the person support apparatus 20to which the actuator is coupled. The amount of braking force that motor68 provides, in at least some embodiments, is up to 10 kilonewtons ormore, when motor 68 is actively braked via controller 70 and/orpassively braked via the closing of fifth switch 76.

In at least one embodiment, controller 70 is modified from that shown inFIG. 3 to oversee and control the operation of all four actuators 32-38.In this embodiment, controller 70 includes sixteen outputs that are eachcoupled to the gates of sixteen different MOSFET switches (four groupsof switches 72 a-72 d). Each group of four switches 72 a-d controls theoperation of one of the motors in one of the actuators 32-38. Controller70 is adapted to allow completely independent control of each of thesefour actuators. That is, controller 70 may brake any one or more of thefour motors of these actuators 32-38 while simultaneously driving anyone or more of the other motors. Further, the speed and direction inwhich each of the four motors 68 are driven is controlled by controller70 independently of the speed and/or direction of the other four motors68. Controller 70 is in electrical communication with one or morecontrol panels—such as, but not limited to, control panel 88 in FIG.1—supported on person support apparatus 20 that include inputs formoving actuators 32-38, and controller 70 carries out the appropriatecontrol of actuators 32-38 in response to these inputs.

Control system 66 ensures that the components of person supportapparatus 20—such as the seat 22, backrest 24, and leg rest 26—arebraked and will not substantially move when power is not being suppliedto the motors 68 or the corresponding actuators. Still further, as hasbeen described above, control system 66 ensures that the braking takesplace regardless of whether or not electrical power is supplied toperson support apparatus 20. Thus, for example, if person supportapparatus 20 has no battery—or the battery becomes drained—and itselectrical power cord is unplugged from an AC wall outlet, passivebraking will still automatically take place via fifth switch 76.Alternatively, if person support apparatus 20 is connected to a sourceof electrical power—whether battery, an AC outlet, or both—controller 70will automatically brake the motors 68 via the appropriate switching ofswitches 72 a-d in H-bridge 74. The components of person supportapparatus 20 therefore do not substantially move when the motors 68 arenot being electrically driven. This helps prevent inadvertent movementand improves the safety of person support apparatus 20. Further, thisenables controller 70, or some other controller, to more easily keeptrack of the current position of each actuator 32-38 by substantiallypreventing movement that might not otherwise be easily detectable, suchas when electrical power is not supplied to person support apparatus 20.

FIG. 7 illustrates in greater detail an alternative motor circuit 82 athat may be incorporated into control system 66 in place of motorcircuit 82. Motor circuit 82 a includes a solid state switch 76 a, acontrol circuit 80 a, and connections to motor 68. Motor circuit 82 adiffers from motor circuit 82 in that it includes solid state switch 76a instead of the electromechanical relay that is used to implementswitch 76. Control circuit 80 a also differs from control circuit 80 inthat it includes a delay circuit 90 a having a resistor 84 a andcapacitor 86 a that are of different values than resistor 84 andcapacitor 86. These different values accommodate the differentelectrical characteristics of solid state switch 76 a. The delayfunction provided by delay circuit 90 a, however, remains the same. Thatis, resistor 84 a and capacitor 86 a define a resistive-capacitive (RC)circuit having a time constant that is determined by the values ofresistor 84 a and capacitor 86 a. When voltage source 78 is terminated,control circuit 80 a continues to supply a positive voltage to oneterminal of solid state switch 76 a for a time generally equal to the RCtime constant of circuit 80 a. This keeps solid state switch 76 a openfor a fraction of a second after electrical power is lost, therebyhelping to prevent damage to any of MOSFETs 72 a-d. After a time equalto or greater than the RC time constant passes, solid state switch 76 areturns to its normally closed state, thereby short circuiting theterminals of motor 68 and braking motor 68 from further movement.

FIG. 8 illustrates a voltage sensing circuit 92 that is included withincontrol system 66 in at least some embodiments. Voltage sensing circuit92 is used by control system 66 to detect when motor 68 is moved when noelectrical power is applied to motor 68. Typically, such movement is dueto mechanical forces being applied to the component (or components) ofperson support apparatus 20 associated with motor 68 that exceed thebraking ability of motor 68. That is, if motor 68 powers backrestactuator 34, for example, a force exerted against backrest 24 when motor68 is not receiving any electrical power from control system 66 willcause a voltage to be generated across the terminals of motor 68 due tomotor 68 acting as a generator. When this applied force reaches a highenough level such that it overcomes the braking force of motor 68, motor68 will begin turning and the back-emf (electromotive force) in motor 68will rise. Voltage sensing circuit 92 senses this rise in the back-emfand feeds it to controller 70, which compares it to a threshold. If thevoltage exceeds the threshold, controller 70 issues a notification tothe user.

More specifically, voltage sensing circuit 92 of FIG. 8 includes twoinputs 94 a and 94 b that are electrically coupled to terminals A and Bof H-bridge 74 of FIG. 5. Inputs 94 a and 94 b are both conditioned andfed to inputs of a comparator 96. Comparator 96 outputs a signal on anoutput line 98 that is directly proportional to the difference, if any,between inputs 94 a and 94 b. The signal on output line 98 is thendigitized and fed to controller 70. Controller 70 reads the digitizedsignal from output line 98 and compares its amplitude to a thresholdvalue stored in a memory. If the amplitude exceeds the stored threshold,controller 70 issues a notification via control panel 88. In someinstances, the notification is an audio and/or visual indication that apotential error has been detected. In other instances, controller 70compares the amplitude of the digitized output from line 98 to a secondand higher threshold, and if the second and higher threshold isexceeded, controller 70 prevents further operation of motor 68 until itscorresponding actuator is recalibrated and/or other corrective measuresare taken by a technician.

In still other embodiments, the signal from line 98 is processed inother manners. For example, in at least one embodiment, the signal fromline 98 is integrated with respect to time and this time integral iscompared to a threshold by controller 70. In still another variation,only those signals on line 98 that exceed a minimum value are integratedand compared to the threshold. In still another embodiment, controller70 uses a maturity counter algorithm that only results in issuing anerror notification if a minimum number of successive readings on outputline 98 are above a threshold. Still other types of filtering andprocessing of the signals on line 98 are possible.

FIG. 9 illustrates an alternative embodiment of a voltage sensingcircuit 92 a that may be used in lieu of the voltage sensing circuit 92of FIG. 8. Voltage sensing circuit 92 a includes an input 100 that iscoupled to one of terminals A and B of H-bridge 74 of FIG. 5. Anothervoltage sensing circuit 92 a that is identical to the one shown in FIG.9 is coupled to the other of the terminals A and B of FIG. 5. Thus, foreach motor 68, two voltage sensing circuits 92 a are utilized: onecoupled to terminal A and the other coupled to terminal B.

Voltage sensing circuit 92 a conditions the input 100 and feeds it to anoutput line 102. Output line 102 is digitized and fed to controller 70.Controller 70 reads the value input on line 102 from the first of thetwo voltage sensing circuits 92 a, reads the value input on line 102from the second of the two voltage sensing circuits 92 a, and determinesthe difference between the two. This difference is then processed in anyof the manners described above and compared to one or more thresholds.If the compared value exceeds one or more of the thresholds, an error isindicated on control panel 88. It can therefore be seen that when usingvoltage sensing circuit 92 a, controller 70 computes the back-emf ofmotor 68 by determining the difference between the output lines 102. Onthe other hand, when using voltage sensing circuit 92, this differenceis determined by comparator 96 and fed into controller 70. Still othertypes of voltage sensing circuits 92, 92 a may be used by control system66, as would be known to one of ordinary skill in the art.

The purpose of voltage sensing circuits 92 or 92 a is to sense if motor68 “drifts” when no electrical power is being applied to it. The term“drift” refers to movement of motor 68 when no electrical power isapplied to motor 68. The detection of such movement is used by controlsystem 66 to determine if motor 68 has moved due to applied physicalforces, rather than electrical current. If such movement is detected,the position of motor 68 will be somewhere other than what is expectedby controller 70. That is, in some embodiments, controller 70 is incommunication with one or more sensors that monitor the movement ofmotor 68, such as, but not limited to, internal Hall-effect sensors.Such sensors provide feedback to controller 70 regarding the position ofmotors 68 when power is applied to the motors 68. However, when themotors are not driven, the sensors do not provide such feedback. Byincluding voltage sensing circuits 92 and/or 92 a, controller 70 is ableto detect movement of the motors 68 when they are not being electricallydriven.

It will be understood by those skilled in the art that the one or morethresholds used by controller 70 in evaluating outputs 98 and/or 102 arebased upon the characteristics of the particular motor 68, as well asthe maximum braking force created by the motor 68 when its terminals areshorted. That is, the enhanced braking power of the motor 68 when itsterminals are shorted is primarily due to the induced current in theshort circuit which, due to Lenz's law, resists movement of motor 68.When motor 68 is effectively resisting an applied force (i.e. not movingin response to the applied force), the voltage generated across theterminals of motor 68 is negligible. However, when more and more forceis applied to motor 68, the windings within motor 68 eventually saturateand motor 68 no longer is able to induce enough current to resistmovement. At that point, motor 68 begins to move and the voltage acrossits terminals increase above the negligible level that otherwise existswhen motor 68 is resisting a smaller applied force. The one or morethresholds used by controller 70 are related to this transition point atwhich motor 68 starts moving in response to an applied force.

In some embodiments, controller 70 is further programmed with one ormore algorithms for converting the back-emf detected by voltage sensingcircuits 92 or 92 a into an estimate of how far motor 68 has moved (e.g.number of revolutions or fractions of revolutions) when electrical poweris not being applied to motor 68. Alternatively, controller 70 may beprogrammed to convert the detected back-emf into an estimate of how farthe corresponding actuator has moved, or an estimate of the currentangle and/or position of the component (e.g. seat 22, backrest 24,and/or leg rest 26) that is moved by the corresponding motor 68. In anyof these embodiments, controller 70 is programmed to carry out theconversion by utilizing data that has been experimentally gathered frommovement of one or more components of person support apparatus 20 whenthe motors 68 are not being driven. By converting the back-emf to adistance, position, and/or angle, controller 70 is able to update acurrent estimate of the position of the motor 68 and/or the component ofperson support apparatus 20 that is moved by motor 68. Thus, controller70 is able to account for the movement of the chair even when suchmovement is due to physical forces applied to the person supportapparatus 20, rather than from the one or more motors 68 being driven.This information is used by controller 70 when moving one or more of themovable components (e.g. seat 22, backrest 24, and/or leg rest 26) ofperson support apparatus 20 to a desired position.

As was noted previously, person support apparatus 20 includes fouractuators: seat actuator 32, backrest actuator 34, lift actuator 36, andleg rest actuator 38. Further, each of these actuators includes a motor68. Controller 70 is programmed to carry out the braking and theback-emf detecting functions described previously for each of thesemotors 68. That is, when actuators 32-38 are to be braked, controller 70short circuits the terminals of each of the four motors 68 associatedwith these four actuators, as discussed above. Further, when these fourmotors 68 are braked, controller 70 monitors each of the four motors 68for back-emf using four separate voltage sensing circuits 92 (or eightvoltage sensing circuits 92 a). In at least one embodiment, controller70 compares the back-emf from each of these four motors 68 to a commonthreshold and issues an error notification if one or more of the motorsexperiences back-emf that exceeds the threshold. In at least one otherembodiment, different thresholds are used for different ones of themotors 68.

Various additional alterations and changes beyond those alreadymentioned herein can be made to the above-described embodiments. Thisdisclosure is presented for illustrative purposes and should not beinterpreted as an exhaustive description of all embodiments or to limitthe scope of the claims to the specific elements illustrated ordescribed in connection with these embodiments. For example, and withoutlimitation, any individual element(s) of the described embodiments maybe replaced by alternative elements that provide substantially similarfunctionality or otherwise provide adequate operation. This includes,for example, presently known alternative elements, such as those thatmight be currently known to one skilled in the art, and alternativeelements that may be developed in the future, such as those that oneskilled in the art might, upon development, recognize as an alternative.Any reference to claim elements in the singular, for example, using thearticles “a,” “an,” “the” or “said,” is not to be construed as limitingthe element to the singular.

What is claimed is:
 1. A person support apparatus comprising: a support surface adapted to support a person thereon; an actuator adapted to move a first component of the person support apparatus with respect to a second component; a motor adapted to drive the actuator; and a control system adapted to brake the motor, the control system further being adapted to: (1) detect a voltage across terminals of the motor when the control system brakes the motor; (2) compare a quantity based on an amplitude of the detected voltage, a duration of the detected voltage, or combination thereof to a threshold; and (3) if the quantity exceeds the threshold, use the quantity to estimate how far the first component has moved while the motor was braked.
 2. The person support apparatus of claim 1 wherein the first component is a backrest adapted to pivot to different angular orientations.
 3. The person support apparatus of claim 1 wherein the control system brakes the motor by short circuiting terminals of the motor.
 4. The person support apparatus of claim 1 wherein the control system is adapted to short circuit terminals of the motor in a first manner using a plurality of switches and in a second manner using a switch different from the plurality of switches, the control system short circuiting the motor in the first manner when electrical power is supplied to the control system and the control system short circuiting the motor in the second manner when electrical power is not supplied to the control system.
 5. The person support apparatus of claim 4 wherein the control system delays short circuiting the motor terminals in the second manner for a predetermined time after electrical power is not supplied to the control system, the predetermined time being based on a resistor-capacitor (RC) circuit.
 6. The person support apparatus of claim 1 wherein the control system includes a plurality of switches arranged in an H-bridge configuration with the motor.
 7. The person support apparatus of claim 6 wherein the control system drives the motor in a first direction by closing a first subset of the plurality of switches and opening a second subset of the plurality of switches, and the control system drives the motor in a second direction opposite the first direction by opening the first subset of switches and closing the second subset of switches.
 8. The person support apparatus of claim 7 wherein the control system brakes the motor by opening at least one of the switches in the first subset and at least one of the switches in the second subset.
 9. The person support apparatus of claim 1 further comprising a sensor adapted to detect movement of the actuator when electrical power is being applied to the motor, wherein the control system uses the sensor to keep track of a position of the actuator when the motor is driven and the control system uses the quantity to update the position when the motor is braked.
 10. The person support apparatus of claim 1 wherein the control system is further configured to use previously gathered experimental data when estimating how far the first component has moved while the motor was braked.
 11. The person support apparatus of claim 10 wherein the person support apparatus is one of a recliner, stretcher, and a bed.
 12. A person support apparatus comprising: a base having a plurality of wheels; a support surface adapted to support a person thereon, the support surface comprising a backrest and a seat; an actuator having a motor adapted to pivot the backrest with respect to the seat; a sensor adapted to detect movement of the backrest when the motor is driven; a voltage sensor adapted to detect a voltage across terminals of the motor when the motor is braked; and a control system adapted to keep track of a position of the backrest using outputs from both the sensor and the voltage sensor, the control system using the outputs from the sensor to keep track of the position of the backrest when the motor is being driven and the control system using the outputs from the voltage sensor to keep track of the position of the backrest when the motor is being braked.
 13. The person support apparatus of claim 12 wherein the sensor is a Hall-effect sensor.
 14. The person support apparatus of claim 12 further comprising: a second actuator having a second motor adapted to move the seat; a second sensor adapted to detect movement of the seat when the second motor is driven; a second voltage sensor adapted to detect a voltage across terminals of the second motor when the second motor is braked; and wherein the control system is further adapted to keep track of a position of the seat using outputs from both the second sensor and the second voltage sensor, the control system using the outputs from the second sensor to keep track of the position of the seat when the second motor is being driven and the control system using the outputs from the second voltage sensor to keep track of the position of the seat when the second motor is being braked.
 15. The person support apparatus of claim 14 wherein the sensor and the second sensor are both Hall-effect sensors.
 16. The person support apparatus of claim 12 wherein the control system is further adapted to perform the following: (1) compute a quantity based on an amplitude, a duration, and/or a combination of the amplitude and duration of a voltage detected by the voltage sensor across the terminals of the motor when the motor is braked; (2) compare the quantity to a threshold; and (3) if the quantity exceeds a threshold, use the quantity to estimate how far the backrest has moved while the motor was braked.
 17. The person support apparatus of claim 16 wherein the control system is further configured to use previously gathered experimental data when estimating how far the backrest has moved while the motor was braked.
 18. The person support apparatus of claim 12 wherein the control system is adapted to short circuit terminals of the motor in a first manner using a plurality of switches and in a second manner using a switch different from the plurality of switches, the control system short circuiting the motor terminals in the first manner when electrical power is supplied to the control system and the control system short circuiting the motor terminals in the second manner when electrical power is not supplied to the control system.
 19. The person support apparatus of claim 12 wherein the control system includes a plurality of switches arranged in an H-bridge configuration with the motor, and the control system drives the motor in a first direction by closing a first subset of the plurality of switches and opening a second subset of the plurality of switches, and the control system drives the motor in a second direction opposite the first direction by opening the first subset of switches and closing the second subset of switches.
 20. The person support apparatus of claim 19 wherein the person support apparatus is one of a recliner, stretcher, and a bed. 